/* File: hello.c */
#include <stdio.h>
int main() {
printf("Hello world\n");
return 0;
}#include <stdio.h>
int main() {
int x = 42;
float pi = 3.14;
char c = 'C';
printf("Results: %d %f %c\n", x, pi, c);
printf("Results: %d %f %c\n", x + 1, pi + 1, c + 1);
return 0;
}Credits: Άρτεμις
#include <stdio.h>
#include <stdlib.h>
// The grade function computes the final grade
// for first year students according to
// https://progintro.github.io
int grade(int final_exam, int homework, int lab){
return final_exam*50/100+homework*30/100+lab*20/100;
}
int main(int argc, char ** argv) {
if (argc != 4) {
printf("Run as: grade final_exam homework lab\n");
return 1;
}
int final_exam = atoi(argv[1]);
int homework = atoi(argv[2]);
int lab = atoi(argv[3]);
int final_grade = grade(final_exam, homework, lab);
printf("My grade is: %d\n", final_grade);
return 0;
}#include <stdio.h>
int main() {
int x = 42, y = 42;
printf("%d %d\n", x++, ++y);
}Credits: Τάσος και Φώτης
#include <stdio.h>
int myround(double x) {
int first = (int) x;
double result = (x - first >= 0.5) ? first + 1 : first;
return result;
}
int main() {
printf("%d\n", myround(42.67));
printf("%d\n", myround(42.499999));
printf("%d\n", myround(42.99));
printf("%d\n", myround(42.50000001));
return 0;
}#include <stdio.h>
int main() {
int x = 43, y = 42;
int max, min;
if (x > y) {
max = x;
min = y;
} else {
max = y;
min = x;
}
printf("%d, %d", min, max);
return 0;
}Credits: Γιώργος
/* Program to compute the sole pythagorean
triplet where a + b + c == 1000. Implements
the solution to https://projecteuler.net/problem=9
*/
#include <stdio.h>
int main() {
// For each combination of a, b, c check
// whether the conditions a + b + c == 1000
// and a^2 + b^2 == c^2 are met
for (int a = 1; a <= 1000; a++) {
for (int b = 1; b <= 1000; b++) {
for (int c = 1; c <= 1000; c++) {
if ((a < b) && (b < c) && (a * a + b * b == c * c) &&
(a + b + c == 1000)) {
printf("a: %d\nb: %d\nc: %d\n", a, b, c);
printf("abc:%d\n", a * b * c);
return 0;
}
}
}
}
return 0;
}/* A small bus simulator that continues to
pick up passengers and report how many
are at each stop. */
#include <stdio.h>
int main() {
int new_passengers, passengers = 0;
int items_read;
while (1) {
printf("How many passengers are going on the bus: ");
items_read = scanf("%d", &new_passengers);
if (items_read == 0 || items_read == EOF) {
break;
}
printf("Items read: %d\n", items_read);
passengers += new_passengers;
printf("Now we have %d total passengers\n", passengers);
}
return 0;
}Credits: Αλέξανδρος
/* Small utility demonstrating the use of srand, rand,
array initialization and looping through array elements
to produce a metric (max element in this case).
*/
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int main() {
int bears[100];
int i;
int max;
// First initialize all array values to random integers
// srand(time(NULL));
srand(100);
for(i = 0; i < 100; i++) {
bears[i] = rand();
}
// Print out all integers
for(i = 0; i < 100; i++) {
printf("%d ", bears[i]);
}
printf("\n");
// Find and the maximum integer
max = bears[0];
for(i = 1; i < 100; i++) {
if(max < bears[i]) {
max = bears[i];
}
}
printf("Max found: %d\n", max);
// things can go wrong when you write out of bounds:
// bears[120000] = 42;
// printf("All good %d\n", bears[120]);
// printf("All good %d\n", bears[100]);
return 0;
}Credits: Στέφανος
/* Short program for computing the factorial
of a number. Does not handle edge-cases
like negative numbers. */
#include <stdio.h>
#include <stdlib.h>
int factorial(int num) {
printf("Computing: factorial(%d)\n", num);
if (num <= 1) {
return 1;
} else {
return num * factorial(num - 1);
}
}
int main(int argc, char ** argv) {
if (argc != 2) {
printf("Run this program as ./factorial <num>\n");
return 1;
}
int num = atoi(argv[1]);
printf("The factorial of this number is: %d\n", factorial(num));
return 0;
}// Program expects *exactly* one argument (so 2 in total including its name)
// And then proceeds iterating through all of argv and printing them as strings.
#include <stdio.h>
int main(int argc, char * argv[]) {
if (argc != 2) {
printf("Usage: %s num1\n", argv[0]);
return 1;
}
int i;
for(i = 0 ; i < argc ; i++) {
printf("%s\n", argv[i]);
}
return 0;
}Credits: Δημήτρης και Δημήτρης
// A small program to test how pointers behave
// and also how is an assignment expression
// evaluated in C.
#include <stdio.h>
int main() {
int *p;
int x[] = {5, 7, 2, 3, 6, 0, 1, 4};
p = x;
while (1) {
printf("p: %p\n", p);
printf("p + 2: %p\n", p + 2);
printf("*p: %d\n", *p);
printf("*(p+2): %d\n", *(p+2));
printf("Value of *p = *(p+2): %d\n", *p = *(p+2)); // try to use +1000000000 instead of +2 and see what happens
if (!(*p)) break;
p++;
}
return 0;
}// Program that allocates and deallocates a 2D array of integers.
#include <stdio.h>
#include <stdlib.h>
int ** create_2d(int rows, int cols) {
int ** array = malloc(rows * sizeof(int *));
if (array == NULL) {
perror("rows malloc");
exit(1);
}
for(int i = 0; i < rows; i++) {
array[i] = malloc(cols * sizeof(int));
if (array[i] == NULL) {
perror("cols malloc");
exit(1);
}
}
return array;
}
void free_2d(int ** array, int rows) {
for(int i = 0; i < rows; i++) {
free(array[i]);
}
free(array);
}
int main() {
int ** array = create_2d(3, 4);
array[0][0] = 1;
free_2d(array, 3);
return 0;
}// Comparing two strings using strcmp vs comparing the pointers (i.e., addresses)
// of two strings. The result is very different.
#include <stdio.h>
#include <string.h>
int main(int argc, char ** argv) {
if (argc != 3) return 1;
printf("strcmp(arg1, arg2): %d %d\n",
strcmp(argv[1], argv[2]), argv[1] == argv[2]);
return 0;
}Credits: Φώτης
// Program to demonstrate finding the average of a
// number of elements in an array and allocating
// elements in different kinds of memory.
#include <stdio.h>
#include <stdlib.h>
double average(int *p, int n) {
int sum = 0;
for (int i = 0; i < n; i++)
sum += *(p + i);
double av = (double)sum / n;
return av;
}
int main(int argc, char **argv) {
int array[100];
int *p = array;
average(array, 100);
int static_array[2][2];
int *ptr_array[2];
ptr_array[0] = malloc(2 * sizeof(int));
ptr_array[1] = malloc(2 * sizeof(int));
printf("static array: %p\n", static_array);
printf("static array[0]: %p\n", static_array[0]);
printf("ptr array: %p\n", ptr_array);
printf("ptr array[0]: %p\n", ptr_array[0]);
}Credits: Άρτεμις
// A program for finding the n-th prime.
#include <stdio.h>
#include <stdlib.h>
long long int loops = 0;
int is_prime(int i) {
int is_first = 1;
for (int j = 2; j*j <= i; j++) {
loops++;
if (i % j == 0) {
is_first = 0;
break;
}
}
return is_first;
}
int main(int argc, char **argv) {
int counter = 0;
int i = 2;
int hold = 2;
int max_prime = atoi(argv[1]);
while (counter < max_prime) {
if (is_prime(i) == 1) {
counter++;
hold = i;
}
i++;
}
printf("Prime number %d is %d\n", max_prime, hold);
printf("Number of loops: %lld\n", loops);
return 0;
}#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#define N 3
#define M 2
int main(void)
{
int **arr, i, j;
arr = malloc(N * sizeof(int*));
for (i = 0; i < N; ++i)
arr[i] = malloc(M * sizeof(int));
for (i = 0; i < N; ++i) {
for (j = 0; j < M; ++j) {
arr[i][j] = time(NULL);
sleep(1);
}
}
for (i = 0; i < N; ++i) {
for (j = 0; j < M; ++j)
printf("%d\t", arr[i][j]);
printf("\n");
}
for (i = 0; i < N; i++)
free(arr[i]);
free(arr);
return 0;
}#include <stdio.h>
#include "primes.h"
int main(void)
{
int a, b;
scanf("%d", &a);
scanf("%d", &b);
printf("%d\n", count_of_prime_numbers(a, b));
return 0;
}#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "primes.h"
int64_t count_of_prime_numbers(int64_t from, int64_t to)
{
if (from > to || from < 1 || to < 1) {
printf("Wrong data\n");
return -1;
}
uint8_t *primes = malloc((to + 1) * sizeof(uint8_t));
if (primes == NULL) {
printf("Malloc failed!\n");
return -1;
}
memset(primes, 1, (to + 1) * sizeof(uint8_t));
primes[0] = 0;
primes[1] = 0;
int i, j;
for (i = 2; i * i <= to; ++i) {
if (!primes[i])
continue;
for (j = i * i; j <= to; j += i)
primes[j] = 0;
}
int64_t count = 0;
for (i = from; i <= to; ++i) {
if (primes[i])
++count;
}
return count;
}Credits: Αλέξανδρος
// Program for computing league scores.
// Possible solution to: https://progintro.github.io/exams/2023/fall/ex13/ - problem #3
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// Datastructure for holding team data
typedef struct {
char name[64]; // including null terminator
int points;
int goals[2]; // in, out
} Team;
// TEST ASAP
// Comparing teams first by points, then by goal difference, last by name
int teamcmp(const void *team1, const void *team2) {
Team *t1 = (Team *)team1; // implicit casting, cry
Team *t2 = (Team *)team2;
if (t1->points != t2->points)
return t2->points - t1->points;
int diff = (t2->goals[0] - t2->goals[1]) - (t1->goals[0] - t1->goals[1]);
if (diff != 0)
return diff;
return strcmp(t1->name, t2->name);
}
// Up to 100 teams, more checks are needed for real world usage
Team teams[100] = {0};
int8_t last_team = 0;
// TODO add helper functions... eventually(tm)
int team_index(char *name) {
int index = -1;
// char found=0; // JUSTICE FOR UNCONDITIONAL JUMPS
for (int i = 0; i < last_team; i++) {
if (strcmp(name, teams[i].name) == 0) {
index = i;
break;
}
}
return index;
}
void add_team(char *name) {
strcpy(teams[last_team].name, name); // ez pwn challenge
last_team++;
}
int main(int argc, char **argv) {
if (argc != 2)
return 1;
FILE *f = fopen(argv[1], "r");
if (!f)
return 1;
char name1[64], name2[64];
int gin, gout;
while (fscanf(f, "%63[^-]-%63[^,],%d-%d\n", name1, name2, &gin, &gout) == 4) {
int team1_index = team_index(name1);
int team2_index = team_index(name2);
if (team1_index == -1) {
add_team(name1);
team1_index = team_index(name1);
}
if (team2_index == -1) {
add_team(name2);
team2_index = team_index(name2);
}
teams[team1_index].goals[0] += gin;
teams[team2_index].goals[0] += gout;
teams[team1_index].goals[1] += gout;
teams[team2_index].goals[1] += gin;
int points = 0;
if (gin > gout) {
teams[team1_index].points += 3;
} else if (gout > gin) {
teams[team2_index].points += 3;
} else {
teams[team1_index].points += 1;
teams[team2_index].points += 1;
}
} // GET OUT
fclose(f);
// Sort out the teams
qsort(teams, last_team, sizeof(Team), &teamcmp);
for (int i = 0; i < last_team; i++) {
fprintf(stdout, "%s, %d, %d - %d\n", teams[i].name, teams[i].points,
teams[i].goals[0], teams[i].goals[1]);
}
return 0;
}